> Habitat & Distribution

Ferrissia fragilis ranges throughout North America from southern Ontario to southern California (Basch 1963; Clarke 1981; Walther et al. 2010) and has been introduced throughout the Old World (Walther et al. 2006).  Populations may inhabit streams, rivers, lakes, ponds, and aquatic habitats of almost any description, on rocks, woody debris, macrophytes and dead leaves.  

Some minimum levels of dissolved oxygen seem to be necessary.  Thus, populations of F. fragilis are not typically found in especially warm or stagnant waters, nor in environments that are artificially enriched or severely polluted.  They are common throughout the Atlantic drainages and the Allegheny and Interior Plateaus of the Midwest, Kentucky and Tennessee, disappearing across the Mississippi River in The Great Plains.  FWGNA incidence rank I-5.

> Ecology & Life History

Ancylids are generally found to be grazers, with diets especially rich in diatoms (Dillon 2000: 77-79).  Blinn et al. (1989) confirmed the importance of diatoms in the diet of a Ferrissia fragilis population inhabiting a pond in Arizona.

Jokinen's (1987) analysis of the distribution of F. fragilis in Connecticut and New York led her to classify it as a “Supertramp” species, found only in the most species-poor communities.  The statewide distribution of F. fragilis documented by Jokinen (1983) suggested to Dillon (2000: 360 - 363) that the species might show Stress-tolerant life history adaptation, allocating an order of magnitude less energy to reproductive effort than expected from body size.  Generation times of less than six weeks have been reported in laboratory populations of F. fragilis, adults maturing around 2-3.0 mm shell length, laying singleton eggs perhaps 0.6 mm in diameter (Basch 1959b, Dillon and Herman 2009).  Jokinen (1985) reported three generations per year for an F. fragilis population in Connecticut (Life cycle E(sis) of Dillon, 2000:159).

Basch (1963) noted that "smaller specimens of F. fragilis are often aphallate, and this situation is also known among the larger Ferrissia."  The allozyme data of Dillon & Herman (2009) suggested that South Carolina populations of F. fragilis are obligately self-fertilizing.  Self-fertilization has also been well-documented in the European freshwater limpet Ancylus fluviatilis (Stadler et al. 1995).

> Taxonomy & Systematics

Basch (1963) recognized five species in the genus Ferrissia - F. rivularis from stones, F. fragilis from vegetation and organic debris in flowing water, F. parallela on narrow-bladed plants in lentic environments, F. walkeri on broad-leaved plants in lentic environments, and F. mcneilli endemic to Alabama.  The shell morphological criteria upon which his system was largely based seem to be subject to a great deal of ecophenotypic plasticity, however (Russell-Hunter et al. 1967, Dillon & Herman 2009).  Walther et al. (2010) combined Basch's five taxa into two species, subsuming parallela under rivularis and walkeri and mcneilli under fragilis.  Ferrissia shimekii (Pilsbry 1890) and Ferrissia hendersoni Walker (1918) are both occasionally encountered junior synonyms of fragilis as well.

Most of the older North American ancylid taxa were initially assigned to either the genus Ancylus or the genus Gundlachia, which were grouped into the subgenus Ferrissia by Walker (1903), and raised to the full genus level in 1917.  Basch (1959c, 1963) synonymized the specific nomen Gundlachia californica (Rowell 1863) under Ferrissia fragilis (Tryon 1863), failing to notice as he did that californica has priority, by five weeks.  For some reason I find difficult to fathom, californica has recently been resurrected from 140 years of obscurity.  We continue to prefer fragilis, for the reasons detailed in my essay of 6Feb19 below.    

> Maps and Supplementary Resources

• Ferrissia distribution in drainages of The Ohio (2019)
• Ancylid distribution in Atlantic drainages (2023)
• Ferrissia distribution in the Tennessee/Cumberland (2022)
• Ferrissia distribution in The Great Plains (2024)
• Virginia species account with county distribution (2011)

> Essays 

• I reviewed the research findings of Andrea Walther and her colleagues suggesting that North America is inhabited by Two Species of Ferrissia on 8Dec10.  The essay includes a couple nice figures comparing rivularis with fragilis.
• See my post of 26Sept14 for good, comparative figures illustrating "The egg masses of freshwater pulmonate snails."
• See my essay of 11Jan17 for an interesting photo of Ferrissia on the back of a Dytiscid beetle - "A previously unrecognized symbiosis?" 
• I justified our preference for the nomen Ferrissia fragilis (Tryon 1863) over californica (Rowell 1863) in my essay of 6Feb19.

> References

Basch, P. (1959a) the anatomy of Laevapex fuscus, a fresh-water limpet (Gastropoda: Pulmonata). Misc. Publ. Mus. Zool. Univ. Michigan 108: 1 - 56.
Basch, P. (1959b)  Studies on the development and reproduction of the fresh-water limpet Ferrissia shimekii (Pilsbry).  Trans. Amer. Micros. Soc. 78: 269 - 276.
Basch, P. (1959c) Status of the genus Gundlachia (Pulmonata: Ancylidae). Occ. Pprs. Mus. Zool. Univ. Michigan 602: 1 - 9.
Basch, P. (1963)  A review of the recent freshwater limpet snails of North America. Bull. Mus. Comp. Zool. Harvard, 129, 399-461. 
Blinn, D., R. Truitt, & A. Pickart. (1989)  Feeding ecology and radular morphology of the freshwater limpet Ferrissia fragilis. J. N. Am. Bentho. Soc., 8: 237-242.   
Burky, A. (1971)  Biomass turnover, respiration, and interpopulation variation in the stream limpet Ferrissia rivularis (Say). Ecol. Monog., 41: 235-251.  
Coffman, W. (1971)  Energy flow in a woodland stream ecosystem: I. Tissue support trophic structure of the autumnal community. Arch. Hydrobiol., 68: 232-276.  
Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs.  Cambridge University Press, United Kingdom.  509 pp.  
Dillon, R. T., & J. J. Herman (2009)  Genetics, shell morphology, and life history of the freshwater pulmonate limpets Ferrissia rivularis and Ferrissia fragilis.  J. Freshwat. Ecol. 24: 261 - 271.  [PDF]
Hubendick, B. (1964) Studies on Ancylidae, The subgroups.  Meddelanden Fran Goteborgs Musei Zoologiska Avendelining, 137.  (Goteborgs Kungl. Vetenskaps-Och Vitterhets-Samhalles Handlingar.  Sjatte Foljden. Ser. B.) 9, 1-72.  
Jokinen, E.  (1983)  The freshwater snails of Connecticut. Hartford, Connecticut, State Geol. Nat. Hist. Survey Bull. 109. 83 p.  
Jokinen, E.  (1985)  Comparative life history patterns within a littoral zone snail community. Verh. Internat. Verein, Limnol., 22: 3292-3399.
Jokinen, E. (1987) Structure of freshwater snail communities: species-area relationships and incidence categories. Am. Malacol. Bull. 5: 9-19.
Keating, S.T. & Prezant, R.S. (1998)  Effects of stream chemistry on the distribution, growth, and diatom colonization of the freshwater limpet, Ferrissia rivularis.  J. Freshwat. Ecol. 13: 67-77.  
Russell-Hunter, W.D., M. L. Apley, A. J. Burky, & R. T. Meadows (1967)  Interpopulation variations in calcium metabolism in the stream limpet, Ferrissia rivularis (Say)  Science 155: 338-340.  
Russell-Hunter, W.D., Burky, A.J. & Russell-Hunter, R.D. (1981)  Interpopulaton Variation in Calcareous and Proteinaceous Shell Components in the Stream Limpet, Ferrissia rivularis.  Malacologia 20: 255-266.  
Stadler, T., S. Weisner, & B. Streit (1995) Outcrossing rates and correlated matings in a predominantly selfing freshwater snail.  Proc. R. Soc. Lond. B 262: 119-125.
Walther, A. C., J. B. Burch and D. O’Foighil (2010)  Molecular phylogenetic revision of the freshwater limpet genus Ferrissia (Planorbidae:Ancylinae) in North America yields two species: Ferrissia (Ferrissia) rivularis and Ferrissia (Kincaidilla) fragilis.  Malacologia 53: 25-45.   
Walther, A. C., T. Lee, J. B. Burch, and D. O'Foighil (2006)  Confirmation that the North American ancylid Ferrissia fragilis (Tryon 1863) is a cryptic invader of European and East Asian freshwater ecosystems.  J. Moll. Stud. 72: 318 - 321.
Walker, B. (1903)  Notes on eastern American ancyli.  Nautilus 17: 13 - 19, 25 - 31.
Walker, B. (1917)  A revision of the classification of the North American patelliform Ancylidae, with descriptions of new species.  The Nautilus 31: 1 - 10.